1. Field of the Invention
The present invention relates to a novel process for producing alcohols through the hydration of olefins. More particularly, the present invention relates to a process for producing alcohols through the direct hydration of olefins characterized by the use of heterogeneous solid catalysts.
2. Description of the Related Art
Vapor and liquid phase reactions have been carried out industrially for the production of alcohols by the direct hydration of olefins.
An examples of the vapor phase reaction is disclosed in Japanese Patent Laid-open No. 3-207728 in which macroporous cation-exchange resin is used as a catalyst. Another example of the vapor phase reaction is disclosed in Japanese Patent Laid-open No. 55-124541 in which a montmorillonite-containing clay is used as a catalyst. More widely industrialized processes use catalysts carrying phosphoric acid on catalyst supports, as disclosed in Japanese Patent Laid-open Nos. 53-84906 and 52-133095 and Japanese Patent Publication No. 51-44915.
In these processes for producing alcohols by using the vapor phase reactions the reaction is generally conducted in a high temperature range to provide less conversion of olefins. These processes thus produce small amounts of alcohol per unit volume of a reactor and require a large amount of non-reacted olefins to be recycled, which is not advantageous considering the facility and energy required. In addition, these common industrial processes using a supported phosphoric acid catalyst are disadvantageous in that the phosphoric acid used as the catalyst component volatilizes during reactions to cause deterioration of the catalytic capabilities.
In this respect, the so-called liquid phase reaction is well-known, which comprises contacting olefins with water in a liquid state, as a solution for the problems inherent to the vapor phase reaction, such as low productivity of alcohols and the necessity for recycling a large amount of non-reacted olefins. For example, Japanese Patent Publication Nos. 43-8104 and 43-16123 disclose a process using an aromatic sulfonic acid as a homogeneous catalyst while Japanese Patent Publication Nos. 49-166, 50-35051 and 49-36204 and Japanese Patent Laid-open No. 53-9746 disclose heteropolyacids as a catalyst.
However, these homogeneous catalysts can be separated and recovered from the mixture of the catalyst and products (especially water, one of the raw materials) through troublesome procedures with much energy required for the treatment. Furthermore, these acid catalysts are uniformly dissolved in the liquid phase and the liquid is thus in contact with a device such as a reactor, with the possibility of corrosion of the inner walls of the reactor. The use of expensive materials for the device is therefore inevitable and hence it is not economical.
To overcome the defects of the homogeneous catalyst mentioned above, heterogeneous solid catalysts have been used in the liquid phase reaction. For example, the use of strong acidic cation exchange resins as catalysts is disclosed in Japanese Patent Publication Nos. 44-26656, 58-7614, and 63-27332 and Japanese Patent Laid-open Nos. 49-117412 and 61-230744. The use of zeolite catalysts is disclosed in International Publication Nos. 3-502321 and 3-503175, Japanese Patent Laid-open Nos. 1-246234, 1-246233 and 63-218251. Strong acidic cation exchange resins have higher activities under the reaction conditions of lower temperature and pressure (about 150.degree. C. and about 100 atm.) in comparison with the homogeneous liquid catalyst mentioned above. However, cation exchange resins themselves have a heat resistance temperature of about 100.degree. C., and hence using them at a temperature of 150.degree. C. means that reactions are performed under constant deterioration of the catalyst and that acidic components such as sulfonic acid are decomposed and eliminated to effuse inevitably into the reaction solutions. The catalytic activities, therefore, are reduced and the effused acidic components have a possibility of corroding the equipment. Accordingly, the use of expensive materials of corrosion resistance is inevitable for the equipment, which is economically disadvantageous. In addition, the cation exchange resins mentioned above are weak in mechanical strength and have a disadvantage of being destroyed during the process.
In comparison with these catalysts, heterogeneous zeolite catalysts are insufficient in their activities and are not expected to have strong catalytic activities comparable to strong acidic cation exchange resins. Moreover, they require high reaction temperature to obtain sufficient yields of alcohols.
Nevertheless, it apparently enhances decomposition of the zeolite compounds and the elimination of aluminum to heat zeolite compounds to a high temperature required for the hydration of olefins in the presence of water in the liquid state. Therefore, the production of alcohols at a desired reaction rate is practically impossible.